Two-Photon Events Discrepant, But What’s the Cause?

Matt Strassler 11/1/11. No rest for the weary: yet another discrepancy. This one is somewhat different from the small multi-lepton excess at CMS of a couple of weeks ago (tenuous, but in a very interesting and plausible place) and from the OPERA faster-than-light neutrino claim (not so tenuous, but not so plausible either). Now we have a discrepancy involving collisions that produce two low-energy photons [particles of light]. The effect is seen in four experiments, not one: both ATLAS and CMS at the Large Hadron Collider (LHC), and also CDF and DZero at the Tevatron collider. It’s too large to be a statistical fluke (the excess is not small and it shows up in four experiments). Nor does it look like an experimental mistake (since it shows up in four experiments). Might it be a sign of a new phenomenon not predicted by the Standard Model (the equations that describe the known particles and forces, plus the simplest possible Higgs particle)? Maybe… Can’t rule it out, though there’s not enough information in the experiments’ public documents for a serious evaluation of that possibility. But in any case, my preliminary impression is that it’s most likely something else: either a problem with the theoretical calculation of what the Standard Model predicts, or a problem with the way this theoretical calculation was used by the experiments.

6 responses to “Two-Photon Events Discrepant, But What’s the Cause?”

I do believe that this is a phenomenon which needs a new interpretation. There are some intrinsic angles, such as, the Cabibbo angel (13.5), Weinberg angle (28.75), neutrino mixing angles. Those mixing angles can also be the channels for photons, not just for quarks or leptons. There are 6 primary mixing angles and 3 secondary angels, such as, 35.84 degrees, 43.91 degrees, 58.19 degrees, etc.). If those excesses happen at those angels, then we know the cause of it.

I highly doubt it. I see discrepancies like this all the time. They do not need new interpretations; typically what happens is that once theorists improve their methods, discrepancies like this go away. Over the years many wrong theoretical and experimental papers have been written trying to introduce new interpretations of the data, when what was actually needed was better predictions. In fact, that’s why many great theorists don’t spend their time tinkering with the Standard Model, and instead focus on improving theorists’ ability to calculate within the Standard Model. If currently we only had the methods that we had 10 years ago, you would have seen far more apparent discrepancies at the LHC than you have already. Fortunately, there has been enormous progress over the last 10 years, which gives us far better predictions than were possible in 2000, and consequently we have far more sensitivity to new phenomena than we used to have.

p.p.s. another famous example: the hint of compositeness of quarks seen at the CDF experiment at Fermilab in 1996 was due to theorists not properly accounting for the unknowns in the structure of the proton, http://www.fnal.gov/whats_new/media_advisory.html

maybe You are right; I like and appreciate Matt`s clear and sound articles and answers a lot too 🙂

And even bearing in mind what I`ve read in the “about me” that he has written more the 75 papers about, I trust him ;-)…
I`m joking (of course) and alluding to a certain answer Matt has given to Plato below a previous article that made me chuckle quite a while … ;-P

Cheers

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A Higgs particle is produced in a proton-proton collision at center, and decays to two photons (particles of light, indicated by green towers) in an LHC detector. Tracks emerging from center are from remnants of the two protons.